Quote Originally Posted by waterbear
first, when you aerate two things happen, the alk goes down and the pH goes up.
Evan,

I have a minor technical correction to this. Even though it is counterintuitive, when there is outgassing of carbon dioxide (from aeration, for example), the pH rises but the Total Alkalinity (TA) does not change at all. See Alkalinity for a good explanation of this. Another way to look at it is that any shift to reduce alkalinity combines a carbonate species (which is basic) with H+ (which is acidic) so there is no net change. This is why Ben's alkalinity lowering technique just increases pH during the aeration phase. It isn't until you add acid that the alkalinity (and pH) get lowered. Believe me, it took me a very long time before this sunk in and I still find it weird!

Richard